The parent patent applications referenced above describe CAS (computer assisted setup) processes and several automatic devices to provide first and second refinements of positions which improve the accuracy of a machine tool table. The advent of these new refinements improve the accuracy of machine tool tables and facilitate in situ inspections on the machine tool table, as disclosed herein.
Inspection of a fabricated part is typically carried out in a separate room, on a separate machine such as a coordinate measuring machine (CMM), after a part has been fabricated.
It is desirable to know the final inspection results prior to the part being fabricated, where CAD (computer assisted design) programs are typically used by a designer to design a part, and CAM (computer assisted manufacture) programs are typically used by a machinist to fabricate and manufacture parts. Inspection prior to fabrication or IPTF is a new CAS process introduced in this patent application where inspection may be carried out before each step of the CAM design for a fabrication process.
Fabrication tools must also be inspected. This inspection of the tools to determine their static geometric dimensions or offsets is typically carried out by an instrument such as a tool pre-setter before the tools have been used.
It is desirable to know the positions of fabricated features in the part that result from the dynamic offsets of the fabrication tools. For example, as the tools wear out during fabrication, the locations of these fabricated features will not be in their desired locations.
These dynamic offsets relate both to the known practice of a static geometrical description of the fabrication tools by a pre-setter, and to the physical result of fabricating a feature into a part. An apparatus and method for determining a third refinement, to automatically improve the accuracy of dynamic offsets and hence of fabricated features, is also disclosed herein.
During manufacture, a quality metric, such as Cpk, may be specified by the designer, near the beginning of the manufacture cycle so as to allow the designer to adjust and optimize the Cpk results during manufacture. This is described in more detail below related to the process for design for manufacture.
Shown in the top view of FIG. 1A is the machine tool table 101 with vise fixed jaw 102 and vise clamping jaw 103 holding a work piece 100. The work piece 100 is constrained in the X axis direction 140 by a probe engaging stop 114, in the Y axis direction 141 by the fixed vise jaw 102, and in the Z axis direction 142 by parallels 109 shown in FIG. 1B.
The probe engaging stop 114 has a reference surface 115 that may be set by a rigid probe 112 held in tool holder 111. The X axis reference position 450 of the spindle axis 106 is determined relative to an X axis electronic gauge block, not shown, as described in the previously cited parent patent applications.
The table has motion X axis direction 104, and motion Y axis direction 105. FIG. 1A also illustrates a tool holder 111, a measuring flexible probe 112 and a spindle 110. Refined positions described in the parent patent applications enable the machine tool table 101 to move in an X axis direction 104, which is in the same direction as the vise reference surface X axis direction 140, and the table motion Y axis direction 105 which is in the same direction as the vise reference surface Y axis direction 141.
FIG. 1B is a front view of the table direction (but not table motion) Z axis direction 142. The vise fixed jaw 102 has a vertical reference surface that also defines the vise Z axis direction 142 as is located in FIG. 1A by the intersection of the X axis 140 and the Y axis 141. The vise Z axis direction 142 is suitable for determining the spindle Z axis direction 106, and is defined by the vise as shown in the FIG. 1B front view when the vise is clamped to the table 101, as is standard machine shop practice.
Also shown in the FIG. 1B is the Z axis 106 for spindle 110 holding a tool holder 111 and measuring flexible probe 112. The spindle 110, tool holder 111 and measuring flexible probe 112 may be rotated about and translated relative to the table 101 in the Z axis direction 106. The determination of Z axis direction 106 is described in the parent patent applications to be parallel to vise Z axis direction 142.
X, Y, and Z, positions may be controlled using instructions with standard g and m codes stored in a memory of the CNC (Computer Numeric Controlled) mill (not shown). A remote computer (not shown) may have an RS-232 cable and a digital cable attached to the CNC mill to provide instructions to control the CNC mill.
Refined X, Y, and Z, positions may be measured by a flexible probe 112 and displayed by X, Y, and Z digital readouts of the CNC mill, not shown, as described in the parent patent applications. These flexible probes typically measure relative position, such as between two reference surfaces on or related to the table 101, and do not determine the X or Y spindle location of Z axis direction 106. As described in the parent patent applications, an electronic gauge block located on the table 101 (not shown in FIG. 1A) utilizing a rigid probe, not shown, comprising a shrink fit tool holder and a gauge pin, is useful to automatically determine the X and Y spindle location of Z axis direction 106. For example as described below in connection with FIG. 4A an X, a Y, and a Z axis electronic gauge block, not shown, together with a rigid probe, not shown, determines an X axis reference surface 450 and Y axis reference surface 460. A Z axis reference surface 470 shown in FIG. 5 is also established.
It is desirable to use the electronic gauge blocks' reference surfaces, probed and set by the rigid probe 112, to determine the location of reference surfaces 450, shown in FIGS. 1, 460, and 470 shown in FIGS. 4A, 4B and 5, and also described in the parent patent applications. The distance between the locations of reference inspection surfaces described herein and reference surfaces 450, 460, and 470 may be probed by measuring flexible probes 112.
Examples of typical measuring flexible probes 112 are made by the companies Renishaw sold by distributor MSC as Renishaw part number A-1036-0100, and made by Swiss Precision Industries (SPI) by distributor Higher Precision as part number 13-145-8. The Renishaw measuring flexible probe 112 has a sphere rather than a cylinder at the measuring tip, and features automatic operation with wireless transmission of the X, Y, and Z measuring information. The manually operated SPI measuring flexible probe 112 has a light that turns on when the cylinder measuring tip touches an X or Y edge.
In addition to measuring flexible probes, there are measuring flexible indicators, also known as dial indicators. These measuring flexible indicators may be held in tool holders, such as tool holder 111. A measuring flexible indicator touches a surface and provides an indication on for example a dial, of the amount of flexure of the indicator tip. An example of a measuring indicator is made by Westward as part number 2YNE2 sold by distributor Grainger. Measuring flexible indicators are useful to measure for example runout of a reference surface to an accuracy of ±0.0001 inches independent from the DRO reading.
It is desirable to hold an SPI measuring flexible probe 112 in a 90 degree fixture, in a tool holder 111, which allows it to measure Z axis positions, not shown in FIG. 1B but described in the detailed description in connection with FIG. 5.
Presently, typical processes for the fabrication and related inspection of the part 100 may call for accuracy at about ±0.005 inches. Typical high end processes for the fabrication of the part 100 may call for accuracy at about ±0.002 inches. Inspection of the part later after the part has been made is unlikely to reveal which step in the fabrication process may be causing an accuracy error.
It is desirable to have high end processes for fabrication and related inspection of part 100 calling for accuracies of about ±0.001 inches, or about ±0.0005 inches or about ±0.0002 inches with an IPTF process for inspection, and hence to know if a fabrication step will cause an error prior to the part 100 being ruined during fabrication in the event something is out of specification.
It is desirable to inspect the part 100 after each new orientation manipulation by the machinist and with an IPTF process to insure the part 100 is properly positioned in the vise. Improper seating is called seating failure, which is described below. Measuring flexible probe 112 is useful to inspect the part 100 for proper position in the vise after each new orientation manipulation, and to use this information to alert the machinist operator in the event something is out of specification with part 100 in the new orientation, with an IPTF process, thereby giving the machinist the chance to remedy the problem before the part may be ruined by the fabrication process.
The X, Y, and Z coordinate system locations with corrections for environmental conditions, referred to in the parent patent applications as the second refinement, can be made available to the machinist by reading the refined X, Y, and Z digital readouts. But this does not tell the whole story as these refined X, Y, and Z digital readouts just define the position of the Z axis 106 center axial location of the spindle 110.
Shown in FIG. 1B is the radius at location 122 of the tip 113 relative to the Z axis 106 location of measuring flexible probe 112 held in the tool holder 111 and spindle 110. This determines a radial offset of the actual X and Y locations of probed positions. This almost tells the whole story as the locations of interest for the probes or cutters have both a radial offset and a Z axis offset from the Z axis 106 center axial location of the spindle 110. For example, the measuring flexible probe tip 113 has point 122 with a radial offset from Z axis 106, and a Z axis offset from reference surface 119 on tool holder 111. In measuring the Y axis runout, the point 122 on measuring flexible probe tip 113 is used to touch points 120 and 121 on fixed vise jaw 102. The machinist refers to the digital readout locations of Z axis direction 106 so that when measuring flexible probe point 122 touches fixed jaw points 120 and 121 there is both a radial offset and a Z axis offset. When the radial offset is subtracted from the Y axis digital readout, and the Z axis offset is subtracted from the Z axis digital readout, then the correct readings for points 120 and 121 are obtained. This technique of subtracting radial offsets, and Z axis offsets, is standard practice for every flexible probe 112 or cutter held in the tool holder 111.
The measuring flexible probe 112 is useful for determining all the points in the refined orthogonal coordinate system that relate to the fabrication of a part 100 by the CNC mill according to an engineering drawing for part 100.
Unfortunately, features machined into part 100 have dynamic edge locations that vary with the cutter rotational speed, the cutter linear speed and direction, the cutter wear, the coolant and lubrication spray on the cutter, the cutter total indicated runout in spindle 110 and of tool holder 111. The cutter diameter will also reduce in size over the life of the cutter, due to cutter wear during fabrication, thereby continuously changing the radial dynamic offset of the cutter.
To tell the whole story, feature edge locations determined by the cutter's static geometrical offsets determined solely by a tool pre-setter, not shown, must be refined by dynamic offsets in order to agree with the desired feature edge locations.
It is desirable to fabricate edge locations of features more accurately with refined dynamic offsets. The accurate determination of these refined dynamic offsets describes the third refinement that improves the accuracy of locations of fabricated features on part 100.
From the machinist's perspective, the definition of the X, Y, and Z axes is first described by an object oriented engineering drawing for the part 100, typically prepared by a designer using a CAD program to define the objects related to part 100. The fabrication of the part 100 may involve the machinist to manipulate the part on the machine tool table vise in the X, Y, and Z axis directions so as to find suitable orientations to optimize the fabrication process typically prepared by a CAM program.
The process for fabrication of part 100 typically uses a CAM software program to determine the time sequenced steps (TSS) performed by the machinist using the CNC mill, and hence to determine the instructions for the CNC mill to fabricate the part 100 according to the engineering drawing for the part 100.
The vise with jaws 102 and 103 is used to hold the part 100 shown in FIG. 1B. The problem then becomes setting up the fixed vise jaw 102, rather than the part 100, to align with the X, Y, and Z axes described above. Once the vise is properly setup and positioned, the proper alignment to hold the part 100 with suitable manipulations in the vise, consistent with the engineering drawing is thereby established.
Failure to be properly positioned in the vise is called seating failure. Detecting seating failure in final inspection after the part 100 has been fabricated is difficult, and unlikely to be linked to the cause of the problem if the part is found to be out of specification in final inspection.
From the designer's perspective the engineering drawing for the part 100 is prepared typically by a CAD software program to determine object oriented features of the part. This may be accomplished by using layers for each object such as for: a coordinate system with multiple origins, construction lines, dimensions, virtual reference objects such as reference surfaces, and features such as holes, pockets, edges, and boundaries. While the designer may have an idea about the time sequence of the fabrication steps of these features, this may not be expressed in the engineering drawing for part 100 other than by specific notes. For example, the specific notes may say “deburr” all edges and thru holes. Furthermore, the designer may not be aware of the exact time sequence of the fabrication steps determined by the machinist on a CAM program.
After submitting the engineering drawing for part 100 to the machinist, the designer typically waits for the part to be delivered by the machinist meeting desired cost, schedule, and accuracy specifications.
It is desirable to notify the designer that there may be a problem, in the event the part may be out of cost, schedule, or accuracy specifications. This feedback step may start prior to fabrication, with the machinist sending a drawing back to the designer, from a machinist's CAS/CAM application to a designer's CAS/CAD application, including each TSS for the engineering drawing for part 100. The intention for these CAS applications is to implement new interactive features designed to work with both the CAM and CAD programs. This will also give the designer the chance to optimize the CAM process with inspections prior to fabrication (IPTF).
In addition to each TSS for fabrication of part 100 optimization, each TSS may be used by the designer to optimize inspections. Since inspection is typically carried out by the machinist after the part 100 is fabricated, in a separate CMM machine, the machinist is responsible for these inspections. Typically the designer performs an incoming inspection after the part has been fabricated on another CMM machine at the designer's facility to verify acceptance of the part 100.
It is desirable for the designer to have input to the inspection process using the CAS/CAD application with new features to optimize inspection at the machinist's facility carried out in situ on the CNC mill with a CAS/CAM application. Both before and after each TSS, using the interactive CAS/CAD and CAS/CAM applications, inspection data give a determination of all specifications including direct linkage to what is possibly causing a fabrication problem after the TSS, and more importantly IPTF inspection data give the best determination as to what may cause a problem before the TSS fabrication is executed. Hence typical inspections may be eliminated both at the machinist's CMM for final inspection and at the designer's CMM for incoming inspection.
Since time is of the essence for the machinist, the CNC mill operations must not be delayed waiting for interactive software programs to respond to each other. It is desirable to use enterprise cloud based applications such as available from IBM®, Oracle®, HP Enterprise®, and Google®, to optimize the data transfer of potentially large data files between CAS/CAD and CAS/CAM applications.
It is also desirable to make it easier for the machinist to interact with the CNC mill to improve the time delay problems. The machinist may prefer to talk to the CNC mill rather than program changes to the CAM program. A voice control microphone and microprocessor available from Knowles as part number IA8508 embed in an electronic gauge block located on the CNC mill table 101 will serve that need and can be implemented in the CAS/CAM application.
Voice control applications may use a virtual assistant. For example the popular Apple® cell phone uses the virtual assistant Siri®.
It is also desirable to have the virtual assistant interact with the machinist with an audible message coming from a speaker. A voice synthesis digital signal processing design platform, Audio Weaver® is available from DSP Concepts® to optimize speaker performance. A voice synthesis application may communicate the inspection results or messages to warn the machinist of fabrication issues related to inspections.
With the confidence that the part may be fabricated and inspected per the design, the designer may also optimize the process for manufacturability. Manufacturability is defined as achieving the best cost metric for a part that meets the specifications. It is desirable to be able to make changes to the design, and get feedback as to the best cost metric of the fabrication as related to manufacturability.
Since there are a large number of TSS combinations, and in addition the complication of using CNC mills with up to 5 axes which further increases TSS complexity, it is desirable to use an artificial intelligence (AI) program. For example the IBM® cloud based applications may use the AI program Watson®, with the capability to solve the TSS complexity problem, where a metric such as a cost, may be optimized for the best TSS order.
Once manufacture of for instance 100 pieces of part 100 starts, there is still more work for the CAS/CAM and CAS/CAD interactive software applications. For example after the first 10 pieces in the manufacturing cycle have been fabricated there is considerable statistical information about how well the specifications are being met. It is desirable to determine the quality metric Cpk for each piece as well as for each of the time sequenced steps for a piece. Review of this inspection information by the designer can result in changes to the design to further optimize the cost, schedule, and accuracy specifications.